1. Field of the Invention
The usefulness of macromolecules to be able to distinguish a specific compound in a complex mixture by binding to a specific compound is the basis for the greatly expanding usefulness of specific binding pair assays, most frequently immunoassays employing antibodies. In the decade spanning 1970-1980, numerous new assays were disclosed in the scientific and patent literature based on a wide variety of different reagents, protocols, and labels. Different approaches were employed to reduce background interference or matrix effects on assay results, to improve labeling techniques, to minimize unmodulatable signals, and to expand the range of sensitivity.
As each new assay has been developed, efforts are made to retain as many of the advantages which have already been realized, while further adding additional advantages. Therefore, there are continued efforts to modify assays which have been demonstrated to have a wide variety of desirable characteristics to enhance one or more characteristics, while substantially retaining the other desirable characteristics.
One group of assays known as "homogeneous" immunoassays relies on the fact that the assays do not require a separation step. Therefore, the assays must be relatively resistant to matrix effects resulting from the physiological fluids, such as blood and urine, which are frequently analyzed. As increasing sensitivity is desired to be able to analyze lower concentrations of a variety of analytes, the matrix or background effects can become extremely troublesome. Therefore, in developing assays of greater sensitivity, it is necessary that they be relatively unaffected by variations in sample composition.
2. Description of the Prior Art
U.S. Pat. No. 4,275,149 described the use of particles in a "homogeneous" immunoassay. Also, a substantial number of references are set forth in the patent. U.S. Pat. Nos. 4,138,213; 4,141,965 and 4,164,558 are illustrative of conventional agglutination techniques for use in immunoassays.